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Noise when Values Open

This is more of a "why is this happening" question than a "how to fix this".

When ever the irrigation system starts, I can hear a noise in the house plumbing and I can't figure out why. It occurs if its a zone for the lawn or one of the drip irrigation circuits.

Here's the setup:
There is about a 75' supply line from the meter at the curb to the house. The line is 1" PVC and transitions to 3/4" copper before entering the basement. Since static pressure is about 75psi, the line immediately leads to a pressure regulator after some Tees for full pressure hose bibbs.

The irrigation system ties into the mainline just after the meter. From there it flows through a "Y" filter and Dual Check Backflow Preventer. From there the line Tees to the manifolds. The first manifold consists of four valves for lawn irrigation. The second manifold consists of four valves for drip irrigation with a 30psi PVC Pressure Regulator between the backflow and valves.

With the exception of drip irrigation lines AFTER the values, everything is 1". Most everything is PVC (except for the brass Backflow) with Rainbird CPF-100 valves.

So why is it that I'm hearing ANYTHING in the house plumbing when these valves located 100-200' of piping away (plus DC) come on?

Sound can travel for miles through water give the right frequency. I know we're not talking dolphins here but something's causing it. =) I'm curious as to the type of sound? Is it a water flowing sound? Maybe a squeal or a bang? Even a grunting sound? Just a guess but since both manifolds cause the sound I'd focus somewhere upstream from those. But I'm not sure. Those valves can be very noisy. Like a grunting sound. It seems to me that there would be much less flow on the manifold with the drip system. I was wondering if the sound in the house is the same from both manifolds? I have no idea what's causing it yet but I'm racking my brain. Good luck!

Sound can travel for miles through water give the right frequency. I know we're not talking dolphins here but something's causing it. =) I'm curious as to the type of sound? Is it a water flowing sound? Maybe a squeal or a bang? Even a grunting sound? Just a guess but since both manifolds cause the sound I'd focus somewhere upstream from those. But I'm not sure. Those valves can be very noisy. Like a grunting sound. It seems to me that there would be much less flow on the manifold with the drip system. I was wondering if the sound in the house is the same from both manifolds? I have no idea what's causing it yet but I'm racking my brain. Good luck!

The sound is not one of running water. But it's difficult to describe.

Based on a similar thead in another forum, the only clue I've got as to what it might be is the sound of the system represurizing after an irrigation valve opens (i.e. water on far side of valve is at 0 psi, so that none-pressure "leaks" back into the system when the valve opens).

Now for what it's worth, I can tell you that I designed this system such that nearly all the water remains in the irrigation lines when the valve shuts off, so I don't get a lot of air pushed out the pipes when the system cuts on, and perhaps my system is repressurizing quicker than a system that is allowed the pipes to drain.

The sound is not one of running water. But it's difficult to describe.

Based on a similar thead in another forum, the only clue I've got as to what it might be is the sound of the system represurizing after an irrigation valve opens (i.e. water on far side of valve is at 0 psi, so that none-pressure "leaks" back into the system when the valve opens).

Now for what it's worth, I can tell you that I designed this system such that nearly all the water remains in the irrigation lines when the valve shuts off, so I don't get a lot of air pushed out the pipes when the system cuts on, and perhaps my system is repressurizing quicker than a system that is allowed the pipes to drain.

The sound is not one of running water. But it's difficult to describe.

Based on a similar thead in another forum, the only clue I've got as to what it might be is the sound of the system represurizing after an irrigation valve opens (i.e. water on far side of valve is at 0 psi, so that none-pressure "leaks" back into the system when the valve opens).

Now for what it's worth, I can tell you that I designed this system such that nearly all the water remains in the irrigation lines when the valve shuts off, so I don't get a lot of air pushed out the pipes when the system cuts on, and perhaps my system is repressurizing quicker than a system that is allowed the pipes to drain.